(1) Field of Invention
The present invention relates to a fuel additives and, more specifically, to a device and method for adjusting the concentration of fuel additive in a hydrocarbon fuel based on simultaneous measurement of the concentration of impurities and additives in the fuel.
(2) Description of Related Art
In the field of fuel additives, it is desirable to inhibit corrosion resulting from the presence of vanadium in hydrocarbon fuels, such as those fuels used in gas turbines and diesel engines. As is widely known, vanadium compounds, in particular vanadyl porphyrins, are naturally occurring in crude oil, heavy fuel oil and related residual fuels (hereafter referred to as “fuel oil”) used to power gas turbines, boilers, diesel engines and similar industrial power-generation equipment (hereafter referred to as “the equipment”). When burned, the Vanadium contaminant forms various vanadium oxides which can cause accelerated corrosion of the metal surfaces in the equipment, such as turbine blades in gas turbines and exhaust valves in diesel engines.
It is widely known that the addition of magnesium-based fuel additives can inhibit the formation of damaging vanadium compounds during combustion and substantially extend the life of the gas turbine or diesel engine, as cited in literature reference numbers 1, 2, and 3 (See the “List of Cited References” below). An example of a commercially available magnesium-based fuel additive is “LMG-30E,” as provided by Liquid Minerals Group, Inc., which located at P.O. Box, 1700, New Waverly, Tex., 77538.
These additives have various proprietary compositions in addition to magnesium, including silicon, aluminum, chromium and other transition-metal compounds, sulphonates and oxides thereof. Typically, in the case of a gas turbine, the equipment operator will test the fuel for contaminants, including vanadium, sodium, potassium and other elements at a specified interval (e.g., every 8 hours) and adjust the rate at which magnesium additive is introduced into the inlet fuel flow based on the concentration of vanadium measured. Magnesium is typically added in the ratio of 3:1 (magnesium:vanadium) by metal weight, although other ratios can be used in some circumstances, for example 3.5:1. However, it is understood that too little magnesium fuel additive will adversely increase the rate of corrosion of the turbine blades, while too much magnesium additive will add cost and result in increased ash buildup, thereby reducing efficiency unnecessarily. It is therefore desirable to precisely monitor the level of vanadium and magnesium additive in the fuel to obtain an optimal operating condition at all times.
The typical method of operation, in which contaminant levels are measured every few hours, can result in substantial errors in fuel additive dosage. This method of operation can be characterized as “open-loop” in the sense that changes in fuel composition or additive dosage rate cannot be detected except when a sample is drawn from the fuel flow and tested in an on-site laboratory. One typical test method is spark emission tomography. This open-loop mode of operation cannot ensure that the equipment is properly protected from excessive contaminant levels at all times.
Thus, a continuing need exists for a device and method that solves the problems of the prior art by continuously and simultaneously monitoring the level of vanadium contaminant and magnesium additive in the inlet fuel stream.